(+)-trans-Chrysanthemic acid (2,2-dimethyl-3-(2-methylprop-1-enyl)cyclopropanecarboxylic acid, 2,2-Dimethyl-3-(2-methylprop-1-enyl)cyclopropane-1-carboxylic acid,
CAS#4638-92-0), is an organic compound that is related to a variety of natural and synthetic insecticides. It is related to the pyrethrin I and II, as well as the pyrethroids.
One of the four stereoisomers, (1R,3R)- or (+)-trans-chrysanthemic acid (pictured), is the acid-derived group of pyrethrin I, which occurs naturally in the seed cases of
Chrysanthemum cinerariaefolium. Many synthetic pyrethroids, for example the allethrins, are esters of all four stereoisomers.

Biosynthesis: Chrysanthemic acid is derived from its
pyrophosphate ester, which in turn is produced naturally from
dimethylallyl diphosphate:

Synthesis: Chrysanthemic acid is produced industrially in a cyclopropanation reaction of a diene as a mixture of cis- and trans isomers, followed by hydrolysis of the ester:

Many pyrethroids are accessible by re-esterification of chrysanthemic acid ethylester.

Uses

Chrysanthemic acid is used for manufacture of DE series household insecticide.